Strange but true: Prisoners barter with mackerel

Check out this terrific story from the Wall Street Journal, about how pouches of mackerel fillets sold at commissaries serve as currency among prisoners in much of the the federal prison system. Short version:

the mack is a good stand-in for the greenback because each can (or pouch) costs about $1 and few — other than weight-lifters craving protein — want to eat it. So inmates stash macks in lockers provided by the prison and use them to buy goods, including illicit ones such as stolen food and home-brewed “prison hooch,” as well as services, such as shoeshines and cell cleaning.